power: remove s3c adc battery driver

The s3c-adc driver is removed along with the s3c24xx platform,
so the battery driver is no longer needed either.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>